The Mark III very-long-baseline interferometry (VLBI) system allows recording and later processing of up to 112 megabits per second from each radio telescope of an interferometer array. For astrometric and geodetic measurements, signals from two radio-frequency bands (2.2 to 2.3 and 8.2 to 8.6 gigahertz) are sampled and recorded simultaneously at all antenna sites. From these dual-band recordings the relative group delays of signals arriving at each pair of sites can be corrected for the contributions due to the ionosphere. For many radio sources for which the signals are sufficiently intense, these group delays can be determined with uncertainties under 50 picoseconds. Relative positions of widely separated antennas and celestial coordinates of radio sources have been determined from such measurements with 1 standard deviation uncertainties of about 5 centimeters and 3 milliseconds of arc, respectively. Sample results are given for the lengths of baselines between three antennas in the United States and three in Europe as well as for the arc lengths between the positions of six extragalactic radio sources. There is no significant evidence of change in any of these quantities. For mapping the brightness distribution of such compact radio sources, signals of a given polarization, or of pairs of orthogonal polarizations, can be recorded in up to 28 contiguous bands each nearly 2 megahertz wide. The ability to record large bandwidths and to link together many large radio telescopes allows detection and study of compact sources with flux densities under 1 millijansky.
Data obtained by the infrared radiometers on the Pioneer 10 and Pioneer 11 spacecraft, over a large range of emission angles, have indicated an effective temperature for Jupiter of 125 degrees +/- 3 degrees K. The implied ratio of planetary thermal emission to solar energy absorbed is 1.9+/-0.2, a value not significantly different from the earth-based estimate of 2.5+/-0.5.
The performance of the GPS user antenna has a great effect on the accuracy and precision of the data that is obtained. This effect is often ignored or misunderstood. This paper presents anechoic chamber measurements of the most important performance characteristics of eight models and configurations of GPS user antennas, and explores the effect of these characteristics on the data collected.
Analysis of 211 very long baseline interferometry observing sessions carried out between November 1979 and August 1984 has yielded estimates of the distances between various radio telescopes located inNorth America and Europe. The average rate of change of the distances between four radio telescopes in North America (Haystack Observatory, Massachusetts' Westford Radio Telescope, Massachusetts; George R. Agassiz Station, Texas' and Owens Valley Radio Observatory, California) and one in Europe (Onsala Space Observatory, Sweden) obtained from the analysis of these data is 19 + 10 mm/yr, where the (68% confidence interval) standard deviation is for the estimate of the rate of change of the Haystack-Onsala baseline length, the one determined most accurately from these data. This estimate of the standard deviation is dominated by the effects of correlated systematic errors due mostly to enors in the model used for the atmospheric delay which we infer introduces errors in each baseline length estimate of 40 mm standard deviation and 60 days correlation time. (By contrast the statistical standard deviation is only 2 mm/yr.) The estimated geologic rates of change of these baseline lengths, averaged over • 10 6 years, are 15 to 17 + 3 mm/yr for the various North American sites to Onsala. Improvements in our model of the atmosphere, and continued monitoring of the distances between North American and European telescopes, will allow the uncertainty of the rate estimates to be reduced over the next few years to a value small compared to our estimated rate of change of these baseline lengths. The use of multiple radio telescopes in Europe will allow us also to separate possible local site motions from plate motions. Paper number 5B5628. 0148-0227/86/005 B-5628 $05.00 and (2) to present the results for the baseline length estimates, their rates of change, and their uncertainties. The effects of the earth's atmosphere on the accuracy of these results are considered in detail by Davis et al. [1985]. 2. MATHEMATICAL AND STATISTICAL MODELS S-439 00 Onsala, Sweden.
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